PHNOM PENH - Cambodia’s opposition on Friday officially reaffirmed its position to boycott an opening session of the National Assembly, saying its demands for a credible investigation into election irregularities have not been met.

The Cambodia National Rescue Party has refused to accept the official results of the election, which gave it 55 National Assembly seats to the ruling party’s 68. Opposition officials say that election fraud cost it a win at the July 28 polls.

By refusing to attend the Sept. 23 meeting, the opposition’s lawmakers-elect threaten to stall the legal formation of a new government.

But at the Rescue Party’s headquarters in Phnom Penh on Friday, party president Sam Rainsy told reporters that “justice” for voters must first be found.

The constitution does not call for the National Assembly’s first post-election session until 60 days after the announcement of official results and not 60 days after Election Day, he said.

The National Election Committee ratified the results of the election on Sept. 8.

That means there is no urgency for an opening Assembly session, Sam Rainsy said.

King Norodom Sihamoni has issued invitation letters to all lawmakers elect, inviting them to join the opening session, presided over by him, on Sept. 23. The king has so far not responded to requests from the opposition for a later date. The ruling Cambodian People’s Party on Thursday responded to the king, saying all 68 of its lawmakers-elect would attend the session.

Kem Sokha, vice president of the Rescue Party, told reporters Friday that the opposition cannot attend the session and must “follow the voters’ will.”

That could include holding more mass rallies, such as those held last week, where up to 20,000 people gathered for three days to call for an investigation into election irregularities.

“If they want us to hold a demonstration again, we will,” Kem Sokha said.